Sesbania sesban improved fallows in eastern Zambia: Their inception, development and farmer enthusiasm

In eastern Zambia, nitrogen deficiency is a major limiting factor for increased food production. Soil fertility has been declining because of nearly continuous maize (Zea mays) cultivation with little or no nutrient inputs. The use of short-duration tree fallows was one of several agroforestry options hypothesized to restore soil fertility. Sesbania sesban, an indigenous N₂-fixing tree was the most promising among species tested in screening trials. Several studies since 1987 have demonstrated the dramatic potential of two- or three-year sesbania fallows in restoring soil fertility and increasing maize yields. Analyses showed that these improved fallow systems were feasible, profitable, and acceptable to farmers. Results suggest that high maize yields following fallows are primarily due to improved N input and availability by the fallows. The potential to increase maize production without applying mineral fertilizers has excited thousands of farmers who are enthusiastically participating in the evaluation of this technology. The number of farmers who are testing a range of improved fallow practices has increased from 200 in 1994 to over 3000 in 1997. Presently, a strong network of institutions comprising government, NGOs, development projects, and farmer organizations is facilitating the adaptive research and expansion of improved fallow technology in eastern Zambia. Key elements in the research process that contributed to the achievements are effective diagnosis of farmers' problems, building on farmers' indigenous knowledge, generating several different fallow options for farmers to test, ex-ante economic analysis, farmer participation in on-farm trials, and development of a network for adaptive research and dissemination.This revised version was published online in November 2005 with corrections to the Cover Date.     

Soil nitrate dynamics in relation to nitrogen source and landscape position in Malawi

Nitrogen is normally the nutrient most limiting production of maize (Zea mays) — the main staple food crop — in southern Africa. We conducted a field study to determine the effect of N sources on soil nitrate dynamics at three landscape positions in farmers' fields in southern Malawi. The landscape positions were dambo valley or bottomland, dambo margin, and steep slopes. The N sources were calcium ammonium nitrate fertilizer applied at 120 kg N ha^–1, biomass from Sesbania sesban, and no added N. Sesbania biomass was produced in situ in the previous season from sesbania relay cropped with maize. Nitrate in the topsoil (0 to 15 cm depth) increased to 85 days after maize planting (mean = 48 kg N ha^–1) and then decreased markedly. Application of N fertilizer and sesbania biomass increased soil nitrate, and nitrate-N in topsoil correlated positively with amount of incorporated sesbania biomass. The strongest correlation between sesbania biomass added before maize planting and topsoil nitrate was observed at 85 days after maize planting. This suggests that the sesbania biomass (mean N content = 2.3%) mineralized slowly. Inorganic N accumulated in the subsoil at the end of the maize cropping season when N fertilizer and sesbania were applied. This study demonstrated the challenges associated with moderate quality organic N sources produced in smallholder farmer's fields. Soil nitrate levels indicated that N was released by sesbania residues in the first year of incorporation, but relay cropping of sesbania with maize may need to be supplemented with appropriately timed application of N fertilizer.This revised version was published online in November 2005 with corrections to the Cover Date.     

Private forest investment and long-run sustainable harvest volumes

Private timberlands in the United States have the biological potential to provide larger quantities of timber on a sustainable basis than they do today. Most opportunities for increasing growth and harvest lie on nonindustrial private lands in the South. Past studies, based on fixed scenarios of future prices, also suggest that many of these opportunities for intensified management can be undertaken with positive economic returns. Translation of these physical and apparent economic potentials into projections of future management and harvest requires a model of private timber management investment behavior. This study examines the dynamics of investment in private forest management according to a model of timber markets and timber supply in which intertemporal levels of private investment, harvest, and timber prices are all endogenous. The results of this model are used to examine the extent and types of possible future private management investments and how these will affect timber supply. In addition, the sensitivity of these projections to variations in key market and behavioral determinants is examined through simulation of alternative scenarios involving reduced public timber harvest and constraints on planting investment of nonindustrial private owners.The base case illustrates the substantial potential of timberlands for increased growth and harvest. This requires, however, investments in planting well beyond those observed in recent years. Given this, the area in planted forests would almost triple within the next 30 years. Expanded investment would allow immediate increases in timber harvest and sustained increases in timber inventory, with virtually no trend in softwood log prices. Projected increases in plantation area would concentrate timber production on fewer hectares, with more hectares managed passively. Naturally regenerated forests in the future would cover at least three-quarters of the private timberland area, with hardwoods continuing to dominate. Restricting nonindustrial private plantation investment to levels observed in the recent past markedly alters projections for softwoods, thus raising prices and reducing timber harvest relative to the base case across the full projection period. In contrast, reductions in public timber harvest alone result in increased prices and reduced total cut in the near term, but have limited impact on the outlook three-five decades hence, because private investment effectively compensates for public timber harvest reductions.     

Management of chronic gangrenous mastitis in a 3-year-old cow using partial (quarter) mastectomy

Bovine gangrenous mastitis is an acute or peracute condition involving one or more quarters of the cow’s udder. It occurs infrequently, but when it occurs, mortality of the affected cows is high. A partial mastectomy of one quarter using a cranial epidural analgesia with 2% lignocaine is described to manage a gangrenous mastitis affecting only one quarter caused by Proteus mirabilis (a gram-negative bacteria) which was not amenable to medical treatment. Partial mastectomy can be a safe and effective procedure for ruminants with udder disease in genetically or otherwise valuable cattle.     

The economics of the carbon sequestration potential of plantation forestry in south-western Uganda

This study assessed the amount of carbon stored and the economic viability of the small-scale Clean Development Mechanism (CDM) carbon offsets in Pinus caribaea and Eucalyptus grandis plantations under varying rotations. Volume equations were used to estimate carbon stocks and merchantable wood volume in the plantations, while net present value (NPV) and annual equivalent value (AEV) were used as measures of profitability at the optimum economic rotation age as well as at the CDM-defined crediting period of 20 years. The findings show that over a 20-year rotation, E. grandis and P. caribaea plantations sequestered 638 and 418 t CO₂-e ha^?1, respectively. The NPVs of E. grandis and P. caribaea with carbon credits over the CDM carbon-crediting period of 20 years were US$2 540 ha^?1 and US$1 814 ha^?1, respectively. This is higher than the NPVs without carbon credits of US$1 543 ha^?1 and US$1 390 ha^?1 for E. grandis and P. caribaea, respectively. The AEV of E. grandis harvested at its optimal economic rotation of 10 years was US$316 ha^?1. This is slightly higher than the AEV of US$298 ha^?1, utilising the CDM carbon-crediting period of 20 years. In contrast, the AEV of P. caribaea under the 20-year CDM carbon-crediting period was higher than harvesting at the optimal economic rotation of 16 years without carbon credits. When the average CDM contract establishment costs exceed US$500 ha^?1 and US$1 000 ha^?1 for P. caribaea and E. grandis woodlots, respectively, it is not economically viable for one to participate in the CDM forest carbon offsets programme. In conclusion, the study results indicate that whereas E. grandis has a higher biological potential to sequester carbon than P. caribaea, it is currently not economically viable for participation in the CDM forest carbon offset scheme. In contrast, it is economically viable for P. caribaea plantations to participate in the CDM, if the CDM contract establishment costs are low.     

The prevalence of porcine cysticercosis in Eastern and Southern provinces of Zambia

The objective of this study was to determine the prevalence and importance of porcine cysticercosis in rural areas of Zambia. The study involved an abattoir survey of 1316 pigs at a slaughter slab in Lusaka and two field surveys in villages in Southern and Eastern provinces. Lingual examination of live pigs and visual inspection of their carcass as well as blood sampling for measuring circulating parasite antigen by enzyme-linked immunosorbent assay (Ag-ELISA) were used as parameters to measure infection. In the field surveys, a questionnaire was administered to every household whose pigs were examined to obtain information on pig husbandry practices and to study risk factors for the infection. Out of the 1316 pigs examined at the slaughter slab, 143 (10.9%) and 271 (20.6%) were positive by lingual examination and meat inspection, respectively. Most of the pigs were very heavily infected with predominantly live cysts. The field surveys revealed that eight (8.2%) out of 98 pigs from Southern province and eight (5.2%) out of 151 pigs from Eastern province were positive for cysticercosis by tongue palpation. Using the Ag-ELISA 20 (20.8%) and 14 (9.3%) pigs were positive in Southern and Eastern provinces, respectively. The questionnaire survey revealed poor pig husbandry practices, absence of meat inspection and control, poor knowledge of the disease and poor sanitation in the surveyed villages. The prevalence of pig cysticercosis found in this study ranks among the highest in the southern African region, in Africa and in the world. The current study suggests the presence of human tapeworm carriers and a high risk of human cysticercosis in the surveyed areas as well as in urban centres where pigs from rural areas are increasingly sold, slaughtered and consumed.     

The serum glucose and beta-hydroxybutyrate levels in sheep with experimental Fasciola hepatica and Fasciola gigantica infection

The influence of Fasciola hepatica and Fasciola gigantica infection on serum glucose and beta-hydroxybutyrate (beta-HOB) in sheep was evaluated. This was done by setting up two groups of sheep. The first group (n=13) was split in two sub-groups, one experimentally infected with F. hepatica (n=9) and the other (n=4) as uninfected control. A second group consisting of a sub-group experimentally infected with F. gigantica (n=9) the other sub-group (n=6) left as uninfected control was also set up. The results of weight gain, parasitological and serum liver enzymes activity (glutamate dehydrogenase [GLDH] and gamma glutamyltransferase [gamma-GT]) used in monitoring the infection showed that all infected animals developed fasciolosis. It was observed that a reduction in serum glucose levels was significantly lower (p<0.05) in F. hepatica infected sheep than in uninfected control sheep starting from 5 weeks post-infection (wpi) to the end of the experiment. Similar reduction was recorded in F. gigantica infected sheep between 8 and 19 wpi. In contrast, serum beta-HOB levels were elevated in F. hepatica infected sheep between 6 and 16 wpi and in F. gigantica infected sheep between 7 and 15 wpi. It would appear from these serum glucose and beta-HOB levels that fasciolosis does lead to energy deficiency (low glucose) and ketosis (increased beta-HOB). The decrease in serum glucose and increase in serum beta-HOB levels in infected sheep may help in understanding the interaction between fasciolosis and nutritional status of infected ruminants especially in young growing animals.     

Climate-driven ecosystem succession in the Sahara: the past 6000 years

Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.